DECOVALEX_IV TASK_D项目的热-水-力耦合过程的数值模拟

核废料地下处置系统研究的国际合作项目DECOVALEX(development of coupled models and their validation against experiments) 致力于高放射性核废料地质处置系统围岩中多个物理场的耦合过程研究和工程屏障的可行性评估.中国研究小组第一次参加DECOVALEX计划.介绍了其子课题Task_D的情况和阶段性研究结果,包括2种处置方式--瑞士FEBEX和美国Yucca Mountain类型的1×104 a以上的预测模拟及其比较分析.建立一套复杂的非饱和多孔介质中热液力(THM)耦合过程的非等温流动和形变控制方程,涉及到固、液、气三相和四种组分(固体骨架,水,干空气和水蒸汽).其表现为相对独立同时又相互交叠的4类模型(1) 考虑有效应力、热膨胀应力和膨润土的水膨胀应力变形模型;(2) 考虑水与蒸汽在蒸发凝结时物质交换的流动模型;(3) 包含蒸汽/干空气相对运动的蒸汽分子扩散和对流模型;(4) 三相局部非等温过程的热交换模型.在此基础上根据Task_D的设定要求简化为较为实用的方程,并发展了相应的程序对1×106 a THM耦合行为进行了预测模拟,其结果在2005年2月Task_D讨论会和DECOVALEX工作会议与多个国家相互独立的研究结果进行对比,吻合程度很高,这给模型的建立和程序发展都带来了信心.     

Preparation and characterization of powellite ceramics Ca1-xLix/2Cex/2MoO4 (0 ≤ x ≤ 1) for Mo-rich HLW condition

Powellite ceramic represent one candidate to immobilize minor actinides and Mo from reprocessed UMo nuclear fuel. In this work, the Ca_1-xLi_x/2Ce_x/2MoO₄ (0 ≤ x ≤ 1) series is prepared via a solid-state reaction using Ce³⁺ as trivalent minor actinide (Am³⁺) surrogate, with structure/microstructure characterized by XRD, XPS, HRTEM, and SEM as well. The Ca_1-xLi_x/2Ce_x/2MoO₄ (0 ≤ x ≤ 1) compositions crystallize in tetragonal and are isostructural with scheelite. Rietveld refinements show that Ce³⁺ and Li⁺ simultaneously enter into the eight-fold coordinated Ca site of powellite crystal. The chemical durability of powellite phases is evaluated by the ASTM C1285-14 product consistency test method B. The leaching behaviours of Ce and Mo are accordance with the interfacial dissolution-reprecipitation mechanism. For all the Ca_1-xLi_x/2Ce_x/2MoO₄ (0 ≤ x ≤ 1) ceramics, 7-days NL_Ce and NL_Mo are found to be in the order of 10⁻³-10⁻⁵ g·m⁻² and 10⁻²-10⁻⁴ g·m⁻² respectively, which exhibit the great retention of Ce and Mo. Interestingly, the values of 7-days NL_Ce and NL_Mo are predominantly controlled by the distortion of MoO₄ tetrahedra and disordered arrangements of Ce³⁺ and Li⁺. Thus, our initial understanding on the structure and chemical durability relation will provide insight to design new waste forms for the Mo-rich HLW condition.     

建议我国重点研究粘土岩处置库预选场址

高放废物地质处置库的围岩选择至关重要.近年来,我国的重点研究对象是花岗岩.作者在列举了国际上正、反两方面的经验教训之后,分析了围岩选择方面的诸多重要因素.在此基础上,建议我国在最终决策前,进一步研究粘土岩处置库作为预选场址.     

高放废液玻璃固化体和矿物固化体性质的比较

对高放废液玻璃固化体和矿物固化体的性能作了比较和分析。矿物固化体较玻璃固化体有下列优势 :体积小、高放废液组分掺入量高、核素浸出率低。高放废液矿物固化体的稳定性分析表明 ,它们十分适合于地下处置库的潮湿和温度变化的环境。虽然单种矿物只能处理部分高放废液组分 ,但多种矿物集合起来可荷载高放废液的全部组分     

Fabrication and basic characterization of silicon nitride ceramics as an inert matrix

Silicon nitride ceramics containing cerium as a simulating element of americium were fabricated to clarify proper sintering conditions. Basic properties of sintered specimens were evaluated for utilization to an inert matrix. Commercial powders of silicon nitride and cerium dioxide (16 or 24.6 wt%), and a powder of aluminum oxide or zirconium oxide as a sintering additive (5 wt%) for some specimens were mixed by ball milling in ethanol. Small amounts of stearic acid as a lubricant were also added. The mixed powder was uniaxially pressed into cylindrical pellets. Then, the pellets were embedded in a packing powder composed of 50 wt%-Si₃N₄ and 50 wt%-BN, and sintered at 2023 or 2073 K for 2 h in a 0.1 MPa N₂ atmosphere. Most of the sintered specimens had high densities (>95% TD). Sintered bodies consisted of columnar silicon nitride grains and grain-boundary phase. XRD analysis clarified that the grain-boundary phase contained crystalline compounds of cerium. The thermal conductivities of sintered specimens except for specimens containing aluminum oxide were about 40 W/m K at room temperature.     

模拟高放玻璃固化体在低氧地下水中的长期蚀变行为研究

高放废物玻璃固化体的长期蚀变行为对深地质处置场的安全评价非常重要。玻璃蚀变在正常条件下发展缓慢,为了能够预测玻璃的长期蚀变行为,本研究采用了150℃下,玻璃体表面积与浸泡溶液体积比(S/V)为6 000 m-1的粉末静态浸泡法(PCT法)来加快腐蚀进度,用扫描电子显微镜-X射线能谱仪(SEM-EDS)和X射线衍射仪(XRD)分析了固体样品表面形貌和二次矿物相,用电感耦合等离子体发射光谱仪(ICP-AES)分析了浸出液中的元素含量。结果表明,模拟高放废物玻璃体在遭受苦咸地下水长期浸泡的后果是表面生成蜂窝状富Mg和Fe的页硅酸盐和铝硅酸盐矿相,这些二次矿相主要是绿脱石[Na0.3Fe2Si4O1(0OH)2.4H2O]、蒙脱石[Ca0.(2Al,Mg)2Si4O1(0OH)2.4H2O]、发光沸石([Na2,K2,Ca)Al2Si10O24.7H2O]和斜发沸石([Na,K,Ca)5Al6Si30O7.218H2O]等矿物。玻璃的溶解进一步加深后,B和Na会以硼砂形式浸出。页硅酸盐矿物的形成会加快玻璃的溶解速度,重新恢复的最大速率要比之前稳定的速率高出约4倍。     

On area-specific underground research laboratory for geological disposal of high-level radioactive waste in China

Underground research laboratories （URLs）, including ＂generic URLs＂ and ＂site-specific URLs＂, are un- derground facilities in which characterisation, testing, technology development, and/or demonstration activities are carried out in support of the development of geological repositories for high-level radioactive waste （HLW） disposal. In addition to the generic URL and site-specific URL, a concept of ＂areaspecific URL＂, or the third type of URL, is proposed in this paper. It is referred to as the facility that is built at a site within an area that is considered as a potential area for HLW repository or built at a place near the future repository site, and may be regarded as a precursor to the development of a repository at the site. It acts as a ＂generic URL＂, but also acts as a ＂site-specific URL＂ to some extent. Considering the current situation in China, the most suitable option is to build an ＂area-specific URL＂ in Beishan area, the first priority region for China＇s high-level waste repository. With this strategy, the goal to build China＇s URL by 2020 mav be achieved, but the time left is limited.     

Pu在地质环境中化学行为的研究进

着重评述了近年来与高放废物深部地质处置有关的地质环境中Pu化学的研究进展,重点讨论了Pu从高放玻璃固化体中的浸出行为、Pu在地下水中的溶解度、配合反应(包括水解反应)、氧化还原反应、胶体的形成等。提出了近期和长期应开展的若干研究课题。     

OPHELIE回填混合物的热-水-力耦合特征

在以比利时高放废物处置参考设计方案的OPHELIE地面大型试验的框架为背景下，进行了一套完整的固结试验项目以获取回填材料的热-水-力反应特征。缓冲材料是预先经高压压实的土块，其主要成分为60%的FoCa泥岩，35%的砂以及5%的石墨（干燥重量），除了对温度和吸力控制设备的简要描述之外，还将阐述有代表性的试验结果，包括持水特性，不同应力，不同吸力，不同温度下的压缩性，膨胀性能，以及在吸湿，吸热条件下的塌陷现象。     

Numerical analysis of thermal process in the near field around vertical disposal of high-level radioactive waste

For deep geological disposal of high-level radioactive waste(HLW)in granite,the temperature on the HLW canisters is commonly designed to be lower than100fiC.This criterion dictates the dimension of the repository.Based on the concept of HLW disposal in vertical boreholes,thermal process in the nearfield(host rock and buffer)surrounding HLW canisters has been simulated by using different methods.The results are drawn as follows:(a)the initial heat power of HLW canisters is the most important and sensitive parameter for evolution of temperaturefield;(b)the thermal properties and variations of the host rock,the engineered buffer,and possible gaps between canister and buffer and host rock are the additional key factors governing the heat transformation;(c)the gaps width and thefilling by water or air determine the temperature offsets between them.